Creatine, one of the most used supplements by athletes

Creatine is one of the most popular supplements among athletes; it is estimated that approximately half of the athletes who participated in the last Olympic Games used it. Creatine (abbreviated frequently as Cr) is a nitrogenous organic acid (also called α-methyl guanidoacetic acid) found in the muscles and nerve cells of some living organisms. It is a derivative of amino acids very similar to them in terms of their molecular structure. Creatine is produced naturally in the human body from amino acids mainly in the kidney and liver, from amino acids such as arginine, glycine and methionine at a rate of one gram of creatine per day (1) Creatine is also found present naturally in foods such as meat (mainly in fish: examples are herring and salmon), dairy products and eggs. It can be found in some vegetables but in very small amounts. It is transported in the blood for the use of muscles. Approximately 95% of the total creatine in the human body is found in the skeletal muscle (2). It is an immediate and direct vector for transporting ATP and providing energy to muscle myofibrils. Cr is an anabolic that is currently used as a dietary supplement in some sports of intensity, due to its ergogenic properties and that allows repetitive loads and brief periods of recovery, with the aim of gaining anaerobic energy (3).

Much of the creatine is stored in all the muscles of the body (around 90%), it is known that an adult who has 70 kg of body weight has about 120 g of creatine. The purpose of storage is the creation, along with phosphorus, of phosphocreatine (PCr), a process in which it consumes ATP. It is present in the muscle cells of vertebrates, as well as some invertebrates, along with the enzyme creatine kinase (4). Muscles are not able to synthesize creatine and that is why they take it from the bloodstream. Phosphocreatine is the immediate and direct source to regenerate ATP (Adenosine triphosphate) an energetic constituent of muscle cells. The levels of both phosphocreatine and ATP in the cell are in equilibrium, although high-intensity training such as the use of dietary supplements containing Creatine mean that in some cases there is a significant increase in intracellular Cr concentrations (5). A similar energy system based on arginine / phosphoarginine operates in many invertebrate animals by similarity, via the action of arginine kinase. One of the functions of Cr is to regulate the pH by means of buffer solutions in the cells.

In studies performed on anaerobic athletes it has been shown that exercise depletes creatine and phosphocreatine reserves at 5-10 seconds, (6) this limit is not clear and there is controversy as other experiments indicate that it can reach up to 20-30 seconds (7). What is true is that no study shows limits greater than one minute. The low level of phosphocreatine is caused by the consumption of ATP reserves in the muscles due to anaerobic exercise and this has as a final, cause muscle fatigue and the inability to perform the exercise until it is replenished. The consumption of Cr supplements causes (according to the studies of the creatine distributors themselves) that phosphocreatine reserves not be depleted so quickly and the anaerobic work period can be maintained for a longer period (8). The scientific studies carried out on the intake of Cr in aerobic athletes show that there are few ergogenic effects in the development and performance of these sports. The reason for this is that the demand and consumption of metabolic energy no longer depends on Cr, but on other sources: lipids or glycogen consumption. It is for this reason, that other mechanisms that do not need creatine are activated: aerobic glycolysis.

Creatine is marketed in the form of a dietary supplement, especially in diets that seek an increase in muscle. Due to its functions related to the re - synthesis of ATP in the muscle in front of efforts of anaerobic origin of high intensity and short duration, creatine supplementation is widely used by athletes. It has been found that an appropriate level of free creatine in the muscle mass of the body facilitates the replacement and preservation of phosphocreatine (9) A person metabolizes approximately 1.2% of the creatine that he stores, that is to say that a 70 kg athlete who spends an amount of 120 to 140 g of creatine in his body, releases approximately two grams of creatine, the losses are compensated with a proper diet.

The transport of ATP to cells can be increased by the simultaneous intake of amino acids (taurine, for example) or carbohydrates, which raise the glycemic index and positively stimulate insulin secretion which in turn stimulates the uptake of creatine by the tissues. Research has been conducted on the uptake of creatine by insulin (10) that show great effectiveness during 24 hours after exercise (11). That effectiveness decreases as the 24 hours pass. It has been shown that vitamin E also improves the ability of transport of creatine to the muscles (12).

One of the most important reasons for the popularity of this supplement among athletes is that it increases their ability to perform high intensity exercise and recover in short periods and with power exercises. In this way they achieve better workouts, and therefore, higher performance. All this depends on the sporting activity that you practice. Creatine is suitable for sprinters or bodybuilders, whose training involves short and intense periods of strength. In aerobic sports such as long distance running, it is believed that Cr could be beneficial in increasing the lactate limit and facilitating rapid recovery, but it is not true. In 20% of cases, athletes who have taken creatine have hardly increased their reserves, which could be due to the fact that they have few fibers of fast contraction, which are the ones that absorb more Cr. In the athletes of long-distance races, who have slow absorption fibers of Cr makes no sense to consume this supplement.

It is very important that the consumed doses of creatine be correct since the effects of Cr depend directly on the increase of total intramuscular Cr, therefore, strategies to expand muscle creatine deposits should be sought as quickly as possible. Excesses of Cr are not absorbed by the body and unnecessarily overload kidney function. The traditional form of administration of Cr supplementation involves two phases: an initial 'load' (which may be around five or six days) followed by a 'maintenance' phase (no longer than two months), followed by a phase of 'rest' similar to maintenance. Dosage metrics have been used as a function of body mass (13) in which they mention 0.25 g / kg / day (ie a quarter of a gram per kilogram of body weight in daily doses) are amounts that show a greater efficiency of Uptake of Cr during the loading phase, while in the maintenance phase should apply a single dose that is one quarter of that used in the loading phase. After the cessation of Cr intake, it takes approximately thirty days to return the blood values prior to supplementation (14). It has not been possible to demonstrate population studies of athletes submitted to Cr intake that affect renal function (15). Cases have been reported in which the intake of creatine has caused gastric disorders (diarrhea), or slight muscle cramps, but there is no sensitive evidence to show its cause. As in any other supplement, it is advisable to consult with your doctor before use.

References

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2. «Creatine». MedLine Plus Supplements. U.S. National Library of Medicine. 20 de julio de 2010. Consultado el 16 de agosto de 2010.
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6. "Suplementación oral de creatina y rendimiento deportivo", Mesa, J.L.; Gutiérrez-Sainz, A. y Castillo, M.J. (2001). Lecturas: Educación Física y Deportes, 36
7. "Conceptos fundamentales acerca de la creatina como suplemento o integrador dietético". Naclerio, F. (2001). Lecturas: Educación Física y Deportes, 30
8. "Effects of creatine supplementation on body composition, strength and sprint perfomance." Kreider, R.B.; Ferreira, M. y Wilson, M. (1998). Medicine and Science in Sports and Exercise, 31, 1770-1777.
9. "Acute creatine cupplementation and performance during a field tests Simulating match play in elite female soccer slayer".Cox, G., Mujika, I., Tumity, D. & Burke, L. nt J. Sports Nutr Exerc. Metabol., 12(1), 33-46. 2002.
10. "Factor Influencing Creatine Loading into human Skeletal Muscle", Snow, R. J. & Murphy, R. M.. Exc sports Sci. Rev, 31(3), 154-158. 2003.
11. "New creatine transporter assay and identification of distintict creatine transporter isoforms in muscle", Walzel, B., Speer, O., Boehm, E., Kristiansen, S., Chan, S., Clarke, K., Magyar, J. P., Richter, E. A. & Wallimann, T.. Am J. Endocrinol Metab, 283, 390-401. 2002.
12. "Efectos de suplementación de creatina en el metabolismo muscular y energético", Rico-Sanz, J.(1997). Archivos de Medicina del Deporte, 61, 391-396.
13. "Effect of creatine and Weight Training on Muscle Creatina and performance in Vegetarians", Burke, D. G., Chilibeck, P. D., Parise, G. C., Andow, D. G., Mahoney, D. & Tarnopolsky, M.. Med. Sci. Sports Exc., Med and Sci. in Sport and Exc.(35), 946-1045. 2003.
14. "Muscle creatine loading in men". Hultman E, Söderlund K, Timmons JA, et al., J Appl Physiol 1996; 81: 232-7
15. "The Effect of Creatine Intake on Renal Function", Kurt A Pline, The Annals of Pharmacotherapy: Vol. 39, No. 6, pp. 1093-1096

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